PURPOSE: To obtain a semiconductor substrate deposited with oxygen in a specified region thereof by providing an insular region for depositing oxygen at the border of a crystal substrate and a thin crystal film and setting the concentration of oxygen within a specified range.

CONSTITUTION: Temperature of a silicon substrate 101 is increased by means of a heating lamp and sustained at 800°C. Oxygen gas is then introduced into a reaction vessel at a rate of 1ml/min while feeding hydrogen gas and that state is held for 1min. Consequently, an oxide 103 having oxygen concentration of 1012-1016/cm2 is deposited on the silicon substrate 101. Oxygen gas supply is then interrupted and monosilane gas is introduced at a rate of 20ml/min along with hydrogen gas thus forming a thin crystal film 103 of 0.5μm thick. This structure enhances the gettering effect for heavy metal contamination.